From requirements for display quality improvements, weight reductions and the like in liquid crystal displays, there is an increasing demand for polymer films with controlled internal molecular orientation structures as optical compensation films such as polarizer plates and retarder plates. With a view to meeting this demand, developments have been made on films making use of optical anisotropy which polymerizable liquid crystal compounds are equipped with.
The term “polymerizable liquid crystal compound” as used herein means a liquid crystal compound, which generally has a polymerizable group and a liquid crystal structure part (a structural part having a spacer moiety and a mesogenic moiety), and as this polymerizable group, an acrylic group is widely employed.
Such a polymerizable liquid crystal compound can be formed into a polymer (film) by a process that irradiates radiation such as ultraviolet rays onto the compound in a liquid crystal state to polymerize the same.
Known processes include, for example, a process that holds a specific polymerizable liquid-crystalline compound having an acrylic group between supports and, while maintaining this compound in a liquid crystal state, irradiates radiation to obtain a polymer (see Patent Document 1); and a process that adds a photopolymerization initiator to a mixture of two polymerizable liquid crystal compounds each having an acrylic group or to a composition, which has been obtained by mixing a chiral liquid crystal to the mixture, and irradiating ultraviolet rays to obtain a polymer (see Patent Document 2).
Polymers (films) obtained by the respective processes are mounted in display devices such as monitors and television sets as polarizer plates, retarder plates and/or the like.
In recent years, the in-cell technology which means the built-in incorporation of external members such as a polarizer plate and a retarder plate has drawn attention as an important element technology for the simplification of next-generation LCD fabrication processes.
Compared with oriented films to be arranged externally, oriented films for use in this in-cell technology are required to show high thermal stability to processes such as high-temperature baking such that their optical anisotropy, transparency and the like remain unchanged. No materials are, however, known at present to be excellent enough to meet this requirement.
Patent Document 1: JP-A 62-70407
Patent Document 2: JP-A 9-208957